When you’re advised to “write what you know,” it’s not so much an absolute rule as a word of caution. Whether you’re crafting the copy for an ad or writing a short story, it’s crucial to have self-awareness when using the voice of characters who come from a background quite different than yours.
This funny Onion advice column from a couple of years back highlights the point beautifully: Ask An Elderly Black Woman As Depicted By A Sophomore Creative Writing Major.
Look over what you’ve written. Have others look it over. Does it sound authentic? Or is it, beyond all hope, cringeworthy and fake?